[LSM Stacking] SELinux policy inside container affects a process on Host

[Leesoo Ahn]

Hello! Here is another weird behavior of lsm stacking..

test env
- Ubuntu 23.04 Ubuntu Kernel v6.2 w/ Stacking patch v38
- boot param: lsm=apparmor,selinux
- AppArmor (Host) + SELinux (LXD Container Fedora 36)

In the test environment mentioned above and applying selinux policy 
enforcing by running "setenforce 1" within the container, executing the 
following command on the host will result in "Permission denied" output.

root at stack-v6:/home/lsahn# insmod 
/lib/modules/6.2.0-20-generic/kernel/net/netfilter/nft_ct.ko
insmod: ERROR: could not insert module 
/lib/modules/6.2.0-20-generic/kernel/net/netfilter/nft_ct.ko: Permission 
denied

In dmesg, the following kernel log is displayed,

[  +0.000003] audit: type=1400 audit(1688619411.654:1072): avc:  denied 
{ module_load } for  pid=67703 comm="insmod" 
path="/usr/lib/modules/6.2.0-20-generic/kernel/net/netfilter/nft_ct.ko" 
dev="sda2" ino=1444804 scontext=system_u:system_r:kernel_t:s0 
tcontext=system_u:object_r:unlabeled_t:s0 tclass=system permissive=0

I have the following questions by the results:
- Why the policy applied within the container affects the host? and 
whether it is a bug or not.
- If this is a bug, I'm curious about where to start the analysis. It 
would be helpful if you could provide relevant resources or links.

best regards,
Leesoo